1. Field of the Invention
The present invention pertains to a lens barrel and, more particularly, to a lens barrel supporting a pair of sub-lens groups, functioning optically when in a mutually close position and in a mutually distant position.
2. Description of the Related Art
In a lens barrel constructed to support a plurality of lens groups, distances between the lens groups must be accurate. This is difficult because the distance between the lens groups is affected not only by the accuracy of the lens itself but also by the accuracy of assembly processes of the lens group frames. Accordingly, the lens distance tend to deviate from one lens barrel to another. While this deviation in the distances may be avoided by providing an adjustment mechanism, provision of such additional mechanisms inevitably leads to larger construction of the lens barrel and an increase in manufacturing costs. Also, adjusting actual distances in each lens barrel is inefficient.
For example, the assignee of the present application has proposed an unprecedented zoom lens system that meets the contradictory demands of high zoom ratio and miniaturization (U.S. patent application Ser. No. 09/534,307, Japanese Patent Application No. Hei 11-79572). This zoom lens system has the following characteristics: it includes a plurality of movable lens groups for varying the focal length; at least one of the lens groups is a switching lens group which includes two sub-lens groups, one of the sub-lens groups being a movable sub-lens group that can be selectively positioned at either one movement extremities in the optical axis direction with respect to the other sub-lens group; the movable sub-lens group of the switching lens group is positioned at an extremity of a short-focal-length zooming range, from the short focal length extremity to an intermediate focal length, and at the opposite extremity of a long-focal-length zooming range, from the intermediate focal length to a long focal length extremity; and zoom paths of the switching lens group and the other lens groups are discontinuous at the intermediate focal length and are defined to focus on a predetermined image plane corresponding to the position of the movable sub-lens group. There may be one or more intermediate focal lengths.
In the mechanical structure of the lens barrel for use in such a zoom lens system, it is desirable to prevent deviation in distance between the sub-lens groups without using an adjustment mechanism in order to avoid a large and complicated switching lens group unit construction, since mechanisms for moving the sub-lens groups toward and away from each other are provided in the support barrel for the switching lens group, which forms a single lens group.
Accordingly, it is an object of the present invention to achieve a lens barrel having a simple construction that can prevent deviation in the distance between the first sub-lens group and the second sub-lens group, wherein the first and second sub-lens groups function optically when in a mutually close position and in a mutually distant position.
In order to achieve the above-mentioned object, a lens barrel includes a front sub-lens group provided on the object side and a rear sub-lens group provided on the image side, the front and rear sub-lens groups functioning optically when in a mutually close position and in a mutually distant position with respect to the optical axes of the front and rear sub-lens groups; a front sub-lens group frame for supporting the front sub-lens group and a rear sub-lens group frame for supporting the rear sub-lens group, the front and rear sub-lens group frames being held in engagement with each other while being able to move in the optical axis direction relative to each other; a lens frame shift mechanism for causing the front sub-lens group frame and the rear sub-lens group frame to move relative to each other to obtain the mutually close position and the mutually distant position; a first lens group positioning surface, provided on the front sub-lens group frame, for positioning the front sub-lens group in the optical axis direction by contacting a portion of a rear surface of the front sub-lens group upon the front sub-lens group being inserted from the front side of the front sub-lens group frame; and a second lens group positioning surface, provided on the rear sub-lens group frame, for positioning the rear sub-lens group in the optical axis direction by contacting a portion of a front surface of the rear sub-lens group upon the rear sub-lens group being inserted from the rear side of the rear sub-lens group frame.
In an embodiment, the front sub-lens group frame includes a front sealed region in the front end portion thereof, the front sealed region preventing the front sub-lens group from coming out from the front side of the front sub-lens group frame. The rear sub-lens group frame includes a rear sealed region in the rear end portion thereof, the rear sealed region preventing the rear sub-lens group from coming out from the rear side of the front sub-lens group frame.
Preferably, the lens barrel further includes a pair of follower engaging recesses which are formed on one of opposing surfaces of the front sub-lens group frame and the rear sub-lens group frame; and a follower projection which are formed on the other of the opposing surfaces of the front sub-lens group frame and the rear sub-lens group frame. The mutually close position of the front sub-lens group is defined via engagement of the follower projection and one of the pair of follower engaging recesses, and the mutually distant position of the front sub-lens group is defined via engagement of the follower projection and the other of the pair of follower engaging recesses.
Preferably, the front sub-lens group frame and the rear sub-lens group frame can be rotated relative to each other. The lens frame shift mechanism includes a shift cam mechanism provided on opposing surfaces of the front sub-lens group frame and the rear sub-lens group frame for moving the front and rear sub-lens group frames to the mutually distant position and to the mutually close position in accordance with the relative rotation of the front and rear sub-lens group frames.
Preferably, the shift cam mechanism includes a shift cam surface provided on one of the opposing surfaces of the front sub-lens group frame and the rear sub-lens group frame, the shift cam surface being inclined with respect to a circumferential direction thereof; and a follower projection provided on the other of the opposing surfaces of the front sub-lens group frame and the rear sub-lens group frame for engaging with the shift cam surface.
Preferably, a pair of follower engaging recesses are formed at opposite ends of each of the shift cam surfaces, wherein the follower projection engages with one of the follower engaging recesses when the front and rear sub-lens group frames are in the mutually close position and in the mutually distant position.
Preferably, the front and rear sub-lens groups form one of a plurality of variable lens groups of a zoom lens system that are moved in the optical axis direction during zooming, the front and rear sub-lens groups serving as a focusing lens group when in the mutually close position and in the mutually distant position. The lens barrel includes a focusing mechanism for moving the front and rear sub-lens group frames in the mutually close position and in the mutually distant position, in the optical axis direction, while maintaining a constant distance between the front and rear sub-lens group frames.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-289388 (filed on Sep. 22, 2000) which is expressly incorporated herein in its entirety.